Muscarinic acetylcholine receptors (mAChRs) are coupled to G-proteins and activate different second messengers and ion channels. Currently, there are five subtypes of mAChRs (M1 to M5) which are differentially distributed throughout the body. mAChRs are involved in a variety of disorders such as irritable bowel syndrome, asthma, glaucoma, cardiac arrhythmia, Parkinson's disease (PD), and Alzheimer's disease (AD). To date, the study of functions and characterization of subtypes of mAChRs are hampered due to lack of highly selective agonists and antagonists. Several toxins which recognize the mAChRs have been purified and sequenced from the venom of mamba snakes of the genus Dendroaspis. The sequences of the toxins are homologous, but their mode of action and selectivity for mAChR subtypes are different. For example, MT-7 is specific only for M1 receptors, whereas MT-3 toxin shows high affinity for M4 receptors, and low affinity for M1 receptors. The structure- activity relationship of MT-7 toxin, therefore, needed to establish the essential amino acid residues responsible for its binding to the M1 receptor to display its functions clearly. Biologically active recombinant MT-7 (rMT-7) toxin is available for such studies. The hypothesis of this proposal is that the functional site of MT-7 toxin requires multiple amino acid residues studies. The hypothesis of this proposal is that the functional site of MT-7 toxin requires multiple amino acid residues which are present in all the three loops of the toxin for its subtype specificity as well as for its action as antagonist. I, therefore propose to study the interaction of MT-7 toxin to M1 receptor, and the Specific Aims of my proposal are. SPECIFIC AIM 1: Production of MT7/MT3 chimeras and MT-7M analogues. SPECIFIC AIM 2: Structure function relationship. SPECIFIC AIM 3: The mode of interaction of MT7/MT3chimeras/MT-7 analogues with M1 receptors. The completion of this study will lead us to establish the critical amino acid residues responsible for MT-7 toxin's binding to its receptor, and will also establish the specific amino acid residues responsible for MT-7 toxin's subtype specificity. The results will help to design therapeutic agents for different disorders involving mAChRs.